Two-axis electromechanical controller

ABSTRACT

An improved two-axis electromechanical controller for controlling a dynamic process is described herein and comprises a hand grip coupled to two gimbal elements having mutually perpendicular axes of rotation, adjustable spring centering means mounted eccentric to the said axes of rotation and an adjustable counterweight for resisting displacement forces on the grip and restoring the grip to a reference position when a displacement force is removed, and electrical transducers for sensing the angular positions of each gimbal element. The force versus displacement relationship of the controller of the described invention is smooth and monotone, and may be adjusted to be substantially linear.

RIGHTS OF THE GOVERNMENT

The invention described herein may be manufactured and used by or forthe Government of the United States for all governmental purposeswithout the payment of any royalty.

BACKGROUND OF THE INVENTION

This invention relates generally to control mechanisms operable abouttwo or more mutually perpendicular axes for mechanically or electricallytransmitting commands for movement in two or more directions. Morespecifically, this invention relates to an electro-mechanical handcontroller comprising two gimbal elements mounted on shafts havingmutually perpendicular axes of rotation, each shaft being suitablyinterconnected to means for generating electrical signals, correspondingto movement of the shafts about their respective axes of rotation, forcontrolling some dynamic process, such as aircraft flight, air refuelingboom control, radar tracking operations, and the like.

Prior art electro-mechanical controllers suffer certain disadvantageslimiting their effectiveness for use such as in aircraft control,because of their vibration sensitivity, high hysteresis characteristicsand inaccurate and erratic operation near the center (or null) position,relatively large displacement required to provide a suitable signal, andlack of suitability for miniaturization to accommodate the space andweight requirements within an aircraft or the like. Additionally,conventional displacement type hand controllers require undesirably highbreakout forces and exhibit high hysteresis and dead-bandcharacteristics. These characteristics contribute to errors making suchcontrollers relatively unsuitable for continuous tracking applications,such as radar tracking, aiming of weapons or sensors, and likeprocesses.

The foregoing problems characteristic of prior art controllers have beeneliminated or significantly reduced in critical importance by theinvention described herein, providing an improved two-axiselectromechanical hand controller for controlling a dynamic process,such as the flight of an aircraft. This invention comprises a controlmember in the form of a hand grip connected to two gimbal elementshaving mutually perpendicular axes of rotation, an adjustable springcentering configuration for the two gimbal elements and an adjustablecounterweight for accurately restoring the grip to a predeterminedreference (null) position when a displacement force is removed, andelectrical transducers for sensing the angular positions of the twogimbal elements and transmitting the appropriate signal to the processbeing controlled.

Accordingly, it is an object of this invention to provide an improvedtwo-axis electromechanical controller.

It is a further object of this invention to provide an improved two-axiselectromechanical controller having an adjustable spring centering meansand adjustable counterweight for accurately and reliably returning thecontroller to the null position when a displacement force is removed.

It is still a further object of this invention to provide an improvedtwo-axis electromechanical controller having no breakout force,hysteresis or dead-band characteristics.

These and other objects of the invention will beecome apparent as thedescription thereof proceeds.

SUMMARY OF THE INVENTION

In accordance with the foregoing principles and objects of the hereindescribed invention, an improved two-axis electromechanical controllerfor controlling a dynamic process is described herein and comprises ahand grip coupled to two gimbal elements having mutually perpendicularaxes of rotation, adjustable spring centering means mounted eccentric tothe said axes of rotation and an adjustable counterweight for resistingdisplacement forces on the grip and restoring the grip to a referenceposition when a displacement force is removed, and electricaltransducers for sensing the angular positions of each gimbel element.The force versus displacement relationship of the controller of thedescribed invention is smooth and monotone, and may be adjusted to besubstantially linear.

DESCRIPTION OF THE DRAWINGS

The invention will be more clearly understood from the followingdetailed description of specific embodiments thereof read in conjunctionwith the accompanying drawings wherein:

FIG. 1 is a perspective drawing of one embodiment of the presentinvention.

FIG. 2 is an isometric drawing of the embodiment of FIG. 1, shown with asubstantial portion of the housing cut away to expose the elements ofthe invention.

DETAILED DESCRIPTION

Referring now to the drawings, FIG. 1 illustrates the controller 1 ofthis invention comprising a conventional control stick 2, and a housing3 providing a support structure for the interior elements of controller1 of this invention. Control stick 2 is connected through verticalextension element 4 to inner gimbal 10 as shown in FIG. 2. Housing 3 hasin the top surface thereof opening 5 of sufficient size to allowsuitable lateral and longitudinal movement of control stick 2.

In FIG. 2, significant portions of the surfaces of housing 3, controlstick 2, and vertical extension element 4 are shown in cutaway to exposethe interior elements of the controller of this invention.

As shown in FIG. 2, the interior elements of controller 1 comprise abalanced rectangular outer gimbal 20 rotatable about axis 21 on shaft 22journalled into and supported by housing 3 through precision ballbearing mounts 23. Inner gimbal 10 is rotatable about axis 11 on shaft12 journalled into and supported by lateral elements 24 of outer gimbal20 through precision ball bearing mounts 13. Inner gimbal 10 issupported within outer gimbal 20 in such manner that axis 11 isperpendicular to, although does not necessarily intersect, axis 21.Downwardly extending portion of inner gimbal 10 comprises an adjustablecounterweight 14 through which, with proper adjustment, the inner gimbal10 may be balanced against the weight of hand grip 2 and verticalextension element 4. The balancing of inner gimbal 10 by means ofadjustable counterweight 14 substantially eliminates the effects ofextraneous acceleration forces on controller 1. In the embodimentconstructed, counterweight 14 comprised a downwardly extending threadedshaft (not shown) attached to inner gimbal 10 for receiving a threadedcounterweight.

Inner gimbal 10 is centered within outer gimbal 20 by means of one ormore centering springs 15 through which inner gimbal 10 may be biased tothe null position against the tension of springs 15. Springs 15 areattached at one end thereof to a rotatable shaft 16 (shown hidden) ininner gimbal 10, shaft 16 being journalled at each end thereof intoinner gimbal 10 through precision ball bearing mounts 17 (also shownhidden). Springs 15 are rigidly attached to prevent slippage thereof onthe surface of shaft 16. Shaft 16 has an axis of rotation parallel toaxis 11 in a plane perpendicular to the centerline of control stick 2and element 4. In the embodiment shown in FIG. 2, shaft 16 is spacedeccentric to axis 11 by approximately one inch, which spacing, thoughnot critical, proved satisfactory for the assembly shown. Springs 15 arerigidly attached at the other ends thereof to spring attaching plate 18such that the tensioning force of springs 15 and the axis of rotation ofshaft 16 and axis 11 lie in the same plane in the null position of innergimbal 10. Plate 18 is in turn adjustably secured at each end thereof tothe lateral elements 24 of outer gimbal 20. Plate 18 may be adjusted toa convenient position within outer gimbal 20 to suitably tension springs15, and then secured into position by conventional means (not shown)such as clamps or set screws. More than one spring 15, though notcritical to the invention herein, may be required to achieve a desiredforce-displacement relationship and a failsafe configuration for innergimbal 10.

Outer gimbal 20 has at one end of its frame a pin 25 locatedeccentrically a convenient distance from shaft 22. In the configurationshown in FIG. 2, a spacing between pin 25 and shaft 22 of one inch,approximately the same spacing between shaft 16 and axis 11 of innergimbal 10, was satisfactory to provide a desired spring attaching radiusfor each gimbal.

Centering springs 26 for outer gimbal 20 are rigidly attached at one endto mounting plate 27 and rigidly attached at the other end to adjustabletensioning plate 28. Rigid attachment of each end of springs 26 isdesired to prevent slippage. Mounting plate 27 is journalled to pin 25through precision ball bearing mount 29. Tensioning plate 28 isadjustably secured to the wall structure of housing 3 by any convenientmeans (not shown) and may be adjusted to a convenient position tosuitably tension centering springs 26. In the configuration shown inFIG. 2, it is desirable for the tensioning forces of centering springs26 to be in a plane perpendicular to axis 21 of rotation of outer gimbal20. Further, more than one centering spring 26, may be desired toachieve a desired force-displacement relationship and fail-safeconfiguration for outer gimbal 20.

The configuration of FIG. 2 shows centering springs 26 and pin 25positioned to one side of shaft 22. This configuration is not criticalto the operation of the controller of this invention, and springs 26 andpin 25 may be otherwise positioned, as for example, below shaft 22, withappropriate changes to housing 3 to accommodate such alternate position.Further, it may be desirable to provide counterweights (not shown) onouter gimbel 20 to dynamically balance outer gimbal 20, against anyvariations in tensioning forces of springs 26.

Shaft 22 of outer gimbal 20 terminates at one end within transducer 30,and, similarly, shaft 12 of inner gimbal 10 terminates within transducer31. In the configuration shown, transducers 30 and 31 are rotaryvariable differential transformers, which provide an electrical outputsignal proportional to the angular displacement of, respectively, shafts22 and 12. Any conventional transducer suitable for the function thereofjust described may be used, but rotary variable differentialtransformers may be preferred in most applications of this inventionbecause they have low internal friction and exhibit substantially nooutput variation due to age and wear. Alternatively, optical transducerscould be used, these also being low friction devices with no backlash.Resistive potentiometers could be used where centering accuracy is notcritical as they exhibit higher internal friction and some backlash.

Spring steel mounts 32 and 33 respectively maintain the housing oftransducer 30 fixed relative to housing 3 and the housing of transducer31 fixed relative to lateral element 24 of outer gimbal 20. Mounts 32and 33 are flexible to accomodate any misalignment of shafts 22 and 12and to eliminate any backlash or hysteresis resulting from any suchmisalignment.

In the assembled configuration as represented in FIG. 2, inner gimbal 10is maintained in a center (or null) position by centering springs 15which have been tensioned through suitable adjusting and securing ofattaching plate 18. Outer gimbal 20 is centered by springs 26 which havebeen tensioned by suitable adjustment of tensioning plate 28.Longitudinal displacement of control stick 2 results in rotation ofinner gimbal 10 about axis 11, causing shaft 16 to be rotated out of theplane originally containing axis 11, shaft 16 and springs 15. Thesprings 15 resiliently resist this displacement. A lateral displacementof control stick 2 results in rotation of outer gimbal 20 about axis 21,causing pin 25 to be displaced. Springs 26 resiliently resist thisdisplacement. When the forces causing the said displacements areremoved, outer gimbal 20 and inner gimbal 10 are restored to the center(or null) positions by the restoring forces of springs 26 and springs15, respectively. In the embodiment constructed, it was found that withsuitable adjustment of attaching plate 18 and tensioning plate 28, asubstantially linear force versus displacement relationship for controlstick 2 was obtained. Transducers 30 and 31 provide appropriate signals,consistent with the respective angular displacements of outer gimbal 20and inner gimbal 10, to control a process. For example, the output oftransducer 30 may control the positioning of ailerons of an aircraft,and the output of transducer 31 may control the positioning of theelevators of the aircraft. Other uses for the controller herein as mightoccur to one with skill in the art are foreseeable.

The invention described herein comprises an improved two-axiscontroller; however, it is understood that a third axis may beincorporated into the controller by providing a control stick rotatableabout its own axis.

Further it is understood that the size, shape and materials ofconstruction of the controller of this invention or of the componentparts thereof may be varied, or the arrangement or the component partsmay be altered within the scope of the appended claims, as might occurto one having skill in the field of this invention, and, therefore allembodiments contemplated hereunder have not been shown in completedetail. Other embodiments may be developed without departing from thespirit and scope of this invention.

We claim:
 1. A two-axis controller which comprises:a. a gimbal mechanismincluding a first rotatable element intercoupled with a second rotatableelement, with the axes of rotation of said first and second rotatableelements being mutually perpendicular; b. a structure for rotatablysupporting said first rotatable element, said first rotatable elementrotatably supporting said second rotatable element; c. a control memberconnected to said second rotatable element; d. a first spring means,interconnecting said structure and said first rotatable element at apoint eccentric to the axis of rotation thereof, for biasing said firstrotatable element to a predetermined reference position; e. a secondspring means, interconnecting said first rotatable element and saidsecond rotatable element at a point eccentric to the axis of rotationthereof, for biasing said second rotatable element to a predeterminedreference position; and f. means for adjustably tensioning said firstspring means and said second spring means.
 2. The two-axis controller asrecited in claim 1 further comprising an adjustable counterweightattached to said second rotatable element for balancing said elementagainst the weight of said control member.
 3. The two-axis controller asrecited in claim 1 or claim 2 further comprising means, connected tosaid first rotatable element, for sensing the rotational displacement ofsaid first rotatable element and providing an electrical output signalproportional thereto, and means, connected to said second rotatableelement, for sensing the rotational displacement of said secondrotatable element and providing an electrical output signal proportionalthereto.